1. Field of the Invention
The present invention relates to a precision roll turning lathe which can machine a three-dimensional pattern, consisting of three-sided or four-sided pyramids arranged in a matrix, in the peripheral surface of a roll.
2. Background Art
Roll grinders and roll turning lathes are generally used as machine tools for machining rolls. A roll grinder includes a headstock, a tail stock, and a carriage which is provided with a grinding wheel.
Such a roll grinder can carry out grinding with a grinding wheel of the peripheral surface of a roll and, in addition, machining of grooves in the peripheral surface. Japanese Patent Laid-Open Publication No. 2003-94239 describes a roll grinder which is provided, in its carriage, with a groove-machining device having a cutting saw blade for groove cutting.
A roll turning lathe is a lathe in which a tool post, having e.g. diamond tools attached thereto, is mounted in a carriage, and is basically used for machining circumferential grooves on a roll by rotating the roll with a headstock and feeding the carriage in the lateral direction (X-axis direction) of the roll. When machining axial grooves on a roll, the carriage is moved at a high speed in the longitudinal direction (Z-axis direction) of the roll while indexing the roll with the headstock (C axis), thereby producing the axial grooves.
The recent progress of machine control technology has realized ultraprecision machining with a lathe, and it has become possible to machine even with a lathe a mold for molding an optical lens. For example, the applicant has proposed a vertical lathe capable of machining a mold for molding of a Fresnel lens (Japanese Patent Laid-Open Publication No. 2004-358624). The vertical lathe can machine with high precision V-shaped lens grooves of a mold for molding of a Fresnel lens.
Owing to the widespread use of liquid crystal displays, there is an increasing demand for lens sheets for use in a backlight of a liquid crystal panel. Such lens sheets include, besides the above-mentioned Fresnel lens, a lenticular lens sheet, a cross lenticular lens sheet, a prism sheet, etc.
Molding a lenticular lens sheet, a cross lenticular lens sheet or a prism sheet by extrusion molding using a transfer roll has recently been studied.
In the case of a transfer roll for the production of a lenticular lens sheet, it is only necessary to machine with precision circumferential grooves at a predetermined pitch in the peripheral surface of the roll. Such machining is possible even with a conventional common roll turning lathe.
On the other hand, in the case of a transfer roll for a cross lenticular lens sheet or a prism sheet, it is necessary to machine a three-dimensional pattern of four-side pyramids or three-sided pyramids on the roll.
For machining of a pattern of four-sided pyramids, cutting of circumferential grooves and axial grooves in a matrix pattern in the surface of a roll is being studied. As regards machining of a pattern of three-sided pyramids, a method is being studied which involves machining axial grooves in combination with spiral grooves in the peripheral surface of a roll.
Conventional roll turning lathes, however, fail to successfully perform ultraprecision machining of such grooves. For example, the headstock of a conventional roll turning lathe, while capable of rotating a roll by means of a motor, does not have both of a roll-rotating function and a roll-indexing function. The conventional lathe thus is incapable of machining axial grooves on a roll.
Though high-precision machining of spiral grooves on a roll is needed to machine a pattern of three-sided pyramids on the roll, there has been no roll turning lathe capable of high-precision screw cutting.